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  Description:  Initialize Communications Port      [PC] [AT] [PS/2]
 
  Initializes a serial communications port to a desired baud rate, parity,
  word length, and number of stop bits.
 
  Input                                    Output
  ═════════════════════════════            ═════════════════════════════════
  AH=00H                                   AH=port status
  AL=initialization parameter              Bit(s)  Significance (if set)
     (see Notes)                           ══════  ══════════════════════
  DX=communications port number            7       timed-out
     (0=COM1, 1=COM2,   etc.)              6       transmit shift
                                                   register empty
                                           5       transmit holding
                                                   register empty
                                           4       break detected
                                           3       framing error detected
                                           2       parity error detected
                                           1       overrun error detected
                                           0       receive data ready
                                           AL=modem status
                                           Bit(s)  Significance (if set)
                                           ══════  ══════════════════════
                                           7       receive line signal
                                                   detect
                                           6       ring indicator
                                           5       data-set-ready
                                           4       clear-to-send
                                           3       change in receive line
                                                   signal detect
                                           2       trailing edge ring
                                                   indicator
                                           1       change in
                                                   data-set-ready status
                                           0       change in
                                                   clear-to-send status
                                    -♦-